Control of leishmaniasis remains a challenge due the high toxicity of the chemotherapeutic drugs presently available. The ongoing search for better leishmanicidal compounds has brought herbal drugs into the limelight as safe and effective substitutes to conventional therapies which have various drawbacks. The current study was designed to evaluate the antileishmanial effect of Quassia amara against Leishmania amazonensis and Leishmania infantum. Different fractions (Hexane (Q1), dichloromethane (Q2), ethyl acetate (Q3) and butanol (Q4)) obtained from the liquid-liquid partition of the crude Q. amara methanol extract were tested against Leishmania promastigote forms. After 120 h of treatment with Q. amara fractions (1 to 500 µg/ml), the minimal inhibitory concentration (MIC) was determined using resazurin. The most active fraction (Q2) was analyzed using thin layer chromatography (TLC) and high performance liquid chromatography-diode array detector (HPLC-DAD) techniques. The effects of Q2 on parasite ultrastructure were investigated by transmission electron microscopy. In addition, Leishmania-infected macrophages were treated with Q2 in order to evaluate the anti-amastigote effect. Among the fractions tested, Q2 showed the highest activity against L. amazonensis and L. infantum promastigotes MIC values of 62.5 and 31.25 µg/ml, respectively. There were ultrastructural alterations, such as nuclear chromatin condensation, intense vacuolization and autophagic and myelin-like figures in parasites treated with Q2 (62.5 µg/ml). Macrophages previously infected with L. amazonensis and L. infantum promastigotes showed a drastic reduction in the number of parasites recovered in the supernatant after Q2 treatment at MIC values. The TLC and HPLC fingerprints of Q2 showed that alkaloids were the main chemical constituents in this fraction. The results presented herein showed that the alkaloid-rich fraction Q2 is a promising source of antileishmanial agents. Further investigation will be necessary in order to isolate and test the substance(s) responsible for the bioactivity.
Key words: Antileishmanial activity, Quassia genus, alkaloids, macrophage infection, nitric oxide.
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